30 Claims, No Drawings ACID ZINC ELECTROPLATING ELECTROLYTE, PROCESS AND ADDITIVE BACKGROUND OF THE INVENTION This invention relates to the deposition of bright zinc electroplate, and more particularly to the electrodeposition of such plate from acid electrolytes.

It is presently recognized that there are certain advantages to being able to plate bright Zinc electrodeposits from acid rather than conventional basic cyanide baths. These advantages include the ability to plate cast iron and carbonitrided steel as well as the avoidance of problems associated with the disposal of toxic cyanide wastes. Thus, a number of processes have been proposed recently for electroplating bright zinc from acid baths which do not contain cyanides.

In operating such acid zinc processes, certain additives are required to obtain bright plate over a commercially operable range of current densities and improved processes, and additives are always desirable to extend this range of operating current densities thus permitting more flexibility in plating, especially in the plating of objects with complex surface configurations.

Certain polyoxyethylene compounds and certain ketone compounds have been proposed for. use in bright acid zinc electroplating, usually in combination with other additives. For example, US. Pat. No. 3,594,291 Todt et al. describes the use of certain ketones with N-polyvinyl pyrrolidone as brighteners in such baths, although the plate produced is not truly bright at high current densities. US. Pat. No. 3,694,330 Korpiun et al. and generally corresponding British Pat. No. 1,149,106 disclose the use, along with an aromatic carbonyl compound and ammonium chloride, of a nonionogenic, surface active polyoxyethylene compound. Suitable aromatic carbonyl compounds are said to include carboxylic acids, carboxylic acid esters, aldehydes and ketones. However, the disclosures do not teach the combined use of both carboxylic acids and ketones but rather the use of them individually as equivalents. The bright plating range is also limited to l to 50 a./ft. although the range below 10 a./ft. is particularly desirable for commercial barrel plating operations.

US. Pat. No. 3,669,854 Harbulak teaches bright acid zinc electroplating using as additives polyethers and at least one nonaromatic a,B-unsaturated carbonyl compound. Harbulak also discloses the use of citric acid as a bath component in addition to the polyoxyethylene compound and a ketone. However, the function of the citric acid is that of a complexing agent rather than that of a brightener. The citric acid maintains the zinc in solution at pHs above 5.5, preventing the precipitation of insoluble zinc salts.

SUMMARY OF THE lNVENTlON The present invention, in certain of its embodiments, provides compositions for acid zinc electrolytic plating baths and additives for such baths, as well as methods for using such baths.

The plating bath compositions of the invention comprise an aqueous bath composition containing at least one zinc compound providing zinc ions for electroplating zinc, a source of chloride ion, at least one nonionic polyoxyethylene compound, at least one ketone, and at least one carboxylic acid, wherein said polyoxyethylene compound is selected from compounds of the formula wherein n m 2 10, x l or 2, derived from a reaction of oxyethylene with a polyol selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7 diol, v polyoxypropylene glycol of molecular weight at least about 900, and I N,N QIQN-tetrakis(polyoxypropylene glycol) ethylene diamine of molecular weight at least about and wherein R is defined by the selected polyol;

said ketone is selected from the group consisting of 4-phenyl-3'buten-2-one (benzalacetone),

4-( 4-methoxyphenyl )-3-buten-2-one (anisalacetone),

4,( 3 ,4-dimethoxyphenyl )-3-buten-2-one (veratralacetone),

4-(3,4-methylenedioxyphenyl)-3-buten-2-one (piperonalacetone), and 4-(2furyl)-3-buten-2-one (furfuralacetone); and

said carboxylic acid is selected from the group consisting of benzoic acid,

cinnamic acid,

Z-furylacrylic acid, and

nicotinic acid.

The polyoxyethylene 2,4,7,9-tetramethyl-5-decyne- 4,7 diol is sold under the name Surfynol" by Air Products and Chemicals, lnc., of Wayne, Pa. The polyoxyethylene polyoxypropylene glycol is sold under the name Pluronic by BASF Wyandotte Corp. of Wyandotte, Michigan. The polyoxyethylene-N,N,N',N'- tetrakis(polyoxypropylene glycol) ethylene diamine is sold under the name Tetronic by BASF Wyandotte Corp.

The bath is preferably operated at a pH between 3.5 and 6.1. The preferred pH range for optimum brightness and operability is 5 to 6. Zinc deposits of acceptable commercial quality can be obtained over the temperature range of 15 to 40C., and the preferred operating temperature range is 20 to 35C. The preferred range of zinc metal content in the bath is 30 to 60 g./l., preferably added as zinc chloride. For best results, the bath should have a total chloride ion content of to g./l., with the major portion (over 50% by weight) of the chloride, other than that derived from zinc chloride, added in the form of ammonium chloride.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS the polyethylene compounds of the invention are used at the same time to obtain the most beneficial results and widest bright plating range.

The operating pH of the bath is established at about 3.5 to 6.1 because at a pH much below 3.5 undesirable dissolution of zinc anodes occurs even without electrolysis, and at a pH much above 6.1 precipitation of insoluble zinc salts commences. In operation, the bath tends to seek its own pH level of about 5.8 to 6.1, and lower pH levels can be maintained only by periodic additions of acid. The higher pH is also desirable in that it minimizes corrosion effects on plated parts due to poor rinsing.

While baths can be operated with the zinc metal content outside the preferred range of 30 to 60 g./I., such conditions are less preferred due to decreasing cathode efficiencies at lower zinc concentrations and increasing low current density dullness at higher concentrations.

The preferred range for total chloride ion content of 150 to I90 g./I. is arrived at from a recognition of the fact that baths containing lower concentrations of chloride, while operable, have the disadvantages of poorer low current density operation, poorer anode corrosion, and a tendency to precipitate insoluble zinc salts at pH's much above 5.5.

It should be recognized that bath formulations may also contain other metal salts such as, for example, potassium sulfate or sodium sulfamate. However, there appears to be little practical advantage to using such materials. Bath formulations may also contain mixtures of zinc salts such as zinc sulfate along with the zinc chloride. Again, there appears to be little or no practical advantage to this, and the preferred range of chloride content of the bath should still be met. If no zinc chloride is used. this chloride should come primarily from ammonium chloride. Alternative sources of zinc include zinc oxide dissolved in common industrial acids such as hydrochloric, sulfuric, acetic, fluoboric, and sulfamic acids. Alternatively, aqueous solutions of commercial zinc salts themselves may be employed, and, as mentioned above, zinc chloride is preferred.

The pH of the bath is adjusted to the desired level by means of addition of ammonium hydroxide, sodium hydroxide or equivalent materials.

The zinc electrode deposits obtained from such acid baths are typically coarse and dull in appearance and have little commercial value until other additives are used. The additive of the invention including certain nonionic polyoxyethylene compounds, certain ketones, and certain carboxylic acids, each component added to the bath in suitable amounts, permits the production of a bright, shiny zinc electrodeposit of a high decorative quality over a wide range of operating current densities and in a higher pH range than taught by the prior art.

As discussed above, the higher pH range is desirable.

Brightener chemicals are preferably added to the bath as two types of additives in order to obtain the correct balance of components for initial start up and subsequent continued maintenance of the bath under optimum conditions of performance.

A starter additive is usually used only once at the start as a new bath is made up. It comprises an aqueous solution containing: polyoxyethylene compounds: I00 to 500 g./l., preferably 200 to 350 g./l.; and carboxylic acid (added as sodium, potassium, ammonium or similar salts) 50 to 250 g./l., preferably to 200 g./I.

A maintenance additive is added initially to the bath and then on demand to maintain performance. It comprises an organoaqueous solution containing: polyoxyethylene compounds 10-400 g./l. preferably 20 to 50 g./l.; carboxylic acid (as sodium, potassium, ammonium or similar salt) 10-200 g./l. preferably 20 to 50 g./l.; and ketone 10 to 200 g./I., preferably 20 to 50 g./l. In the maintenance additive, methanol is used to solubilize the sparingly soluble ketones of the invention. The amount of methanol required varies depending on the concentration of ketone used in the formulation, but typically may comprise 30 to 50 percent by weight of the formulation. In place of methanol other inexpensive organic solvents such as ethanol, acetone and the like may be employed.

In practicing the invention in the start up of a new bath, the desired amount of starter additive, typically l0 to 40 cc. per liter of bath, is added to the bath and well mixed. Next the desired amount of maintenance additive typically 10 to 40 cc. per liter of bath is added to the bath and well mixed. The bath is now ready for operation.

To illustrate the operation of the invention and its superiority over the prior art, the experiments were performed which are set forth in the following examples. In the examples, an aqueous bath containing 75 g./l. ZnCI and g./l. NH CI was used. The temperature of operation was about 20C. The pH and other parameters, and the additives used and their concentrations are stated in the examples, and the resulting characteristics of plates at various current densities are set forth. For the polyoxyethylene compounds, the approximate molar content of the polyoxyethylene is given.

A variety of parts including nuts, bolts, washers, safety harness clamps were barrel plated in a horizontal barrel for 20-30 minutes. Loading varied from 900-1,800 grams and plating current from 20-45 amps. Bright, shiny, well-adherent zinc with good coverage in recesses was obtained on all parts.

Various other parts radio speakers, radio chassis, chain, wheel rims were rack plated in the same bath using average current densities of 20-60 a./ft. and air agitation. Again, bright, shiny, well-adherent zinc with good coverage in recesses was obtained on all parts.

I claim:

1. A composition for providing bright zinc electrode deposits which comprises an aqueous acidic electrolyte composition containing at least one zinc compound providing zinc ions for electroplating zinc, a source of chloride ion, 0.05 to 20 g./l. of at least one nonionic wherein n m I 10, x l or 2, derived from a reaction of oxyethylene with a polyol selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7 diol,

polyoxypropylene glycol of molecular weight at least about 900, and

N ,N,N',N-tetrakis(polyoxypropylene glycol) ethylene diamine of molecular weight at least about 500, and wherein R is defined by the selected polyol;

said ketone being selected from the group consisting of 4-phenyl-3-buten-2-one, 4-(4-methoxyphenyl)-3-buten-2-one, 4-(3,4-dimethoxyphenyl)-3-buten-2-one, 4-(3,4-methylenedioxyphenyl)-3-buten-2-one, and 4-(2-furyl)-3-buten-2-one; and

said carboxylic acid being selected from the group consisting of benzoic acid,

cinnamic acid,

2-furylacrylic acid, and

nicotinic acid.

2. A composition according to claim 1 having a zinc metal content within the range of about 30 to 60 g./l. with the zinc added as zinc chloride, a total chloride ion content of about 150 to I90 g./l. with the chloride other than zinc chloride being added in the form of ammonium chloride, a pH in the range of about 3.5 to 6.1, the polyoxyethylene compounds being present in the range of about 0.05 to 20 g./l., the ketone being present in the range of about 0.05 to 2 g./l., and the carboxylic acid being present in the range of about 0.05 to 20 g./l.

3. A composition according to claim 2 having a pH in the range of about 5 to 6, a content of polyoxyethylene compounds in the range of about 2 to 10 g./l., a ketone content of about 0.1 to 0.5 g./l., and a carboxylic acid content of about 1 to 6 g./l. wherein said polyoxyethylene compounds are polyoxyethylene 2,4,7,9- tetramethyl-5-decyne-4,7 diol and said ketone is 4-phenyl-3-buten-2-one.

4. A composition according to claim 1 wherein the polyol is 2,4,7,9-tetramethyl-5-decyne-4,7 diol.

5. A composition according to claim 1 wherein the polyol is polyoxypropylene glycol of molecular weight of at least 900.

6. A composition according to claim 1 wherein the polyol is N,N,N,N'-tetrakis(polyoxypropylene glycol) ethylene diamine of molecular weight at least about 500.

7. A composition according to claim 1 wherein said ketone is 4-phenyl-3-buten-2-one.

8. A composition according to claim 1 wherein said ketone is 4-(4-methoxyphenyl)-3-buten-2-one.

9. A composition according to claim 1 wherein said ketone is 4-(3,4-dimethoxyphenyl)-3-buten-2-one.

10. A composition according to claim 1 wherein said ketone is 4-(3,4-methylenedioxyphenyl)-3-buten- 2-one.

11. A composition according to claim I wherein said ketone is 4-(2-furyl)-3-buten-2-one.

12. A composition according to claim 1 wherein said carboxylic acid is benzoic acid.

13. A composition according to claim 1 in which the pH is in the range of about 3.5 to 6.1.

14. A composition according to claim 1 wherein the zinc concentration measured as metal is in the range of about 30 to 60 g./I., and the zinc is provided as zinc chloride. I

15. A composition according to claim 1 wherein the bath has a total chloride ion concentration of about 150 to l g./l., with the major portion of the chloride being provided as zinc chloride and ammonium chloride.

16. A composition according to claim 1 wherein the polyoxyethylene compounds are present in a concentration range of about 2 to 10 g./l.

17. A composition according to claim 1 wherein the ketone is present in concentration range of about 0.1 to 0.5 g./l.

18. A composition according to claim 1 wherein the carboxylic acid is present in a concentration range of about 1 to 6 g./l.

19. A method of producing bright zinc electrodeposits which comprises passing current from an anode to a cathode at a temperature about in the range of 15 to 40C. through an aqueous acidic electrolyte composition containing at least one zinc compound providing zinc ions for electroplating zinc, a source of chloride ion, 0.05 to 20 g./l. of at least one nonionic polyoxyethylene compound, 0.05 to 2 g./l. of at least one ketone, and 0.05 to 20 g./l. of at least one carboxylic acid,

said polyoxyethylene compound being selected from compounds of the formula wherein n m 10, x l or 2, derived from a reaction of oxyethylene with a polyol selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7 diol,

said ketone being selected from the group consisting of 4-phenyl-3-buten-2-one,

4-(4-methoxyphenyl)-3-buten-2-one,

4-( 3 ,4-dimethoxyphenyl )-3-buten-2-one,

4-(3,4-methylenedioxyphenyl)-3-buten-2-one, and

4-(2 furyl)-3-buten-2-one; and

said carboxylic acid being selected from the group consisting of benzoic acid,

cinnamic acid,

Z-furylacrylic acid, and

nicotinic acid.

20. A method of claim 19 operated at temperatures in the range of to 40C. with a zinc metal content within the range of about 30 to 60 g./l., the zinc being added as zinc chloride, a total chloride ion content of about 150 to 190 g./l. with the chloride other than zinc chloride being added in the form of ammonium chloride, a pH in the range of about 3.5 to 6.1, the polyoxy ethylene compounds being present in the range of about 0.05 to g./l., the ketone being present in the range of about 0.05 to 2 g./l., and the carboxylic acid being present in the range of about 0.05 to 20 g./l.

21. A method of claim 20 having a pH in the range of about 5 to 6, a content of polyoxyethylene compounds in the range of about 2 to 10 g./l., a ketone content of about 0.1 to 0.5 g./l., and a carboxylic acid content of about 1 to 6 g./l. wherein said polyoxyethylene compounds are polyoxyethylene 2,4,7,9-tetramethyl-5- decyne-4,7 diol and said ketone is 4-phenyl-3-buten- 2-one.

22. A method of claim 19 wherein the pH is in the range of about 3.5 to 6.1.

23. A method of claim 19 wherein the zinc concentration measured as metal is in the range of about 30 to 60 g./l., and the zinc isprovided as zinc chloride.

24. A method of claim 19 wherein the bath has a total chloride ion concentration of about ISO to I90 g./l., with the major portion of the chloride being provided as zinc chloride and ammonium chloride.

25. A method of claim 19 wherein the polyoxyethylene compounds are present in a concentration range of about 2 to 10 g./l.

26. A method of claim 19 wherein the ketone is present in a concentration range of about 0.1 to 0.5 g./l.

27. A method of claim 19 wherein the carboxylic acid is present in a concentration range of about 1 to 6 g./l.

28. An organoaqueous-addition agent for use in preparing an acid zinc electroplating bath composition, said addition agent comprising:

10 to 400 g./l. of at least one nonionic polyoxyethylene compound selected from the group consisting of wherein n m 10, x 1 or 2, derived from a reaction of oxyethylene with a-polyol selected from the group consisting of..

2,4,7,9-tetramethyl-5-decyne-4,7 diol,

polyoxypropylene glycol of molecular weight at least about 900, and

N,N,N',N-tetrakis(polyoxypropylene glycol) ethylthe polyoxyethylene compounds are polyoxyethylene- 2,4,7,9-tetramethyl-5-decyne-4,7 diols, the ketone is 4-phenyl-3-buten-2-one, and the carboxylic acid is benzoic acid.

30. An addition agent according to claim 29 contain- I ing 20 to 50 g./l. of the polyoxyethylene compounds, 20 to 50 g./l. of the ketone, and 20 to 50 g./l. of the carboxylic acid.